This invention relates to a fuel supply system for direct injection engines and more particularly to an improved fuel supply system for an outboard motor incorporating a direct injection system.
As is well known, in all fields of engine design there is an increasing emphasis on obtaining more effective emission control, better fuel economy and, at the same time, continued high or higher power output. This trend has resulted in the substitution of fuel injection systems for carburetors as the engine charge former. In order to obtain still further improvements, direct fuel injection systems are being considered. These systems inject fuel directly into the combustion chamber and thus have significant potential advantages.
In many applications, the incorporation of direct injection is relatively straightforward. However, in connection with outboard motors, the very compact nature of the outboard motor renders this further sophistication in engine design difficult to obtain. The problems in connection with direct fuel injection systems for outboard motors is related primarily to the space that is.
These problems arise, in part, because of the number of components required for fuel injection and the very nature of some of these components. For example, with manifold injection systems for outboard motors, it has been the practice to provide a fuel injection system that includes at last the following components:
a low pressure fuel pump,
a high pressure fuel pump,
a pressure regulator,
a vapor separator; and
a fuel rail for delivering the fuel to the injectors.
The use of a vapor separator is required primarily because of the confined space and the fact that fuel vapors or air in the fuel, conditions primarily resulting from heat, can cause erratic injection and poor performance.
For the same reasons, it has also been the practice to position the high pressure fuel pump in the vapor separator so as to permit it being cooled and to minimize the amount of heat that is generated in the system and to remove the heat from the fuel that is delivered to the injectors. This also saves space. However, this necessitates the use of an electrically operated fuel pump. Such pumps have has limited capacity in the pressure which they can generate.
With direct injection systems, however, the fuel must be injected directly into the combustion chamber. This means that the pressure into which the fuel is injected is higher than with manifold injection systems wherein the pressure is at substantially atmospheric or even below. Electric pumps are not totally capable of supplying such high pressures.
In order to supply the necessary pressures for a direct cylinder injection, it has been proposed to employ a fuel supply system of the type used with manifold injection systems. This is comprised of an engine driven pump which supplies fuel to a vapor separator in which the electrically operated fuel pump is provided. However, fuel is supplied from this pump to a mechanical pump that is driven off of the engine and which can generate higher pressures as required by the direct injection system. This type of system can be quite effective.
However, it is also generally the practice to provide an arrangement in the fuel system where the system can be pressurized to test it for leaks. In addition, it is desirable to have a system wherein the fuel pressure can be released from the system in order to facilitate servicing and/or disassembly without having the fuel spurt out of the system. Where pumps of the type employing both an electric high pressure and an even higher pressure mechanical pump, this an provide a very complicated arrangement since each must be provided with its own testing and bleeding system.
It is, therefore, a principle object of this invention to provide an improved fuel supply system for a direct injected internal combustion engine, and particularly one that is utilized in an outboard motor application.
It is a further object of this invention to provide an improved high pressure system wherein testing and pressure relief can be simply accomplished and the number of valves and fittings to achieve this are substantially reduced.
In one form of manifolding for supplying fuel to the fuel injectors of an engine, there is provided a vertically extending fuel rail that connects to a series of vertically spaced fuel injectors. The fuel rail extends vertically in an outboard motor because unlike normal applications, the engine rotates with its crankshaft journaled about a vertically extending axis. This means that the cylinders are spaced vertically from each other rather than horizontally with normal engine applications.
It has been the practice to supply the fuel to the fuel rail at the lower end thereof and to provide a pressure relief valve at the upper end that relieves the pressure by bypassing the fuel back to the system upstream of the pump. Although these arrangements have some advantages, it must be borne in mind that outboard motors may be used relatively infrequently with some time intervals between use.
Since it is desirable to reduce the pressure in the system when the engine is not running, this means that the fuel is frequently drained or relieved from the fuel rail and other components during times when the system is not being used. Bleeding the air from the system for a start up after periods of no-use is quite difficult with the prior art type of arrangements.
It is, therefore, a still further object of this invention to provide an improved fuel delivery system for an internal combustion engine having a direct injection system and particularly when utilized in connection with an outboard motor wherein the components are arranged so as to provide a self-bleeding operation upon start up after a period of non-use.
It is a further object of this invention to provide an improved and simplified fuel manifold and fuel supply system for an outboard motor having a direct fuel injection system.
A first feature of this invention is adapted to be employed in a fuel supply system for a direct injected internal combustion engine. The fuel supply system includes a fuel storage tank and a first pressure pump for drawing fuel from the tank and elevating its pressure to a first level. A second higher pressure pump is in communication with the first pump and is adapted to receive the fuel from the first pump and to elevate its pressure to a higher pressure for delivery to a direct cylinder fuel injector. In accordance with this feature of the invention, a system is provided for bypassing the fuel delivered by the first pump past the second pump so that the pressure systems of both pumps can be tested from a single location.
Another feature of the invention is adapted to be embodied in a fuel supply system for supplying fuel to a direct injected outboard motor having a plurality of vertically spaced cylinders, each of which is supplied with fuel from a respective one of a plurality of vertically spaced fuel injectors. A fuel supply system is provided that includes a vertically extending fuel rail connected to the fuel injectors is provided for supplying fuel to the injectors. The fuel supply system has both a pressure inlet port and a pressure return port formed at the upper end thereof, and which ports are disposed above the uppermost fuel injector served by the fuel rail.